Better understanding of how societal, behavioral, and environmental conditions interact with diverse genetic backgrounds will allow at-risk populations with an increased susceptibility to obesity to be targeted for preventive measures. Also, the prescription of customized obesity treatment assignments will increase the likelihood of successful interventions and the restoration of health. In addition, the reduction of cardiovascular risk factors will improve morbidity and mortality in this population, and result in a reduction in the cost of health care. This study aims to examine and compare lifestyle, cardiovascular risk, health status, and genetic background in two populations for a total of 2000 individuals: half with BMI >40 kg/m2 and half <30 kg/m2. Diet, body composition, lifestyle, cardiovascular risk factors, and the prevalence of polymorphisms in genes known to affect body habitus, energy intake or expenditure will be assessed and compared. High throughput genotyping will allow the examination of DNA and the determination of polymorphism prevalence in this racially and ethnically diverse cohort. Obese subjects will then undergo a one year period of treatment at a obesity clinic with a protocol selected by the patient and their attending physician, response to treatment monitored, and variability in response examined for the influence of genetic factors. This research project attempts a collaborative, multidisciplinary approach linking biomedical, social, and behavioral science in order to clarify the potential role of genetic-environmental interactions in obesity treatment.